Elastic or stretchable strands have found considerable use, especially in the disposable garment industry. The term "disposable garment" is meant to refer to articles intended to be worn only once or temporarily, with ultimate disposal rather than laundering. Examples include: diapers; adult incontinence garments; hospital garments such as surgical gowns, caps or shoe covers; disposable pajamas; laboratory coats; shower caps and similar items. Generally, such garments are made of lightweight film or sheet material such as: thermoplastic materials; non-woven coated films or papers; or, composites of one or more of these types of materials. Since low cost manufacture is generally a critical requirement, such garments are often manufactured using techniques such as die-cutting, adhesive-bonding, heat-sealing and sonic-sealing; rather than through application of stitching or sewing methods utilized in more expensive, longer-lasting, textile garments.
It has been found desirable in such garments to provide elastic constructions in the vicinity of openings, such as to accommodate a wearer's arm, neck, waist, head or leg. Elasticity in these portions of the garment accomplishes numerous functions including: insuring snug fit for a variety of sizes of users; and, in instances such as disposable baby diapers, providing for a sealing or containing construction, for example around a baby's legs, to prevent or reduce leakage.
Two primary, related, forms of providing for elasticized openings have been developed. In a first of these an elastic member is stretched and is attached to the article in an elastically contractible condition. After attachment to the article, tension is released and the elastic strand contracts, bunching up or shirring the article. A strand, for example, so attached around a leg opening will cause the leg opening to contract. If the contracted leg opening is smaller in diameter than a leg projecting therethrough during use, in such use the elastic member will be stretched open somewhat, and will press snugly against the leg member, generating a snug fit or closing relationship.
A variety of methods of attachment of the elastic member to the garment or substrate have been developed. These include heat-sealing, sonic welding and pressure-sensitive adhesives or the like. In some instances spaced adhesive units have been utilized to advantage, in providing for relative strength or preferred shirring patterns.
A variety of elastic strand constructions, for utilization as described above, have been developed. Included in these are single strand arrangements. A problem with such arrangements is that they are relatively susceptible to problems with failure, unless made relatively strong. A reason for this is that the failure of a single point of attachment or adhesion can cause a complete product failure. Further, should the single elastic member fracture or break, substantially complete failure may also result.
Another problem with a single strand arrangement is that only a relatively narrow seal or closure is formed; and, if made relatively tight, irritation to the wearer's skin in a very narrow, localized, region or band may result.
As a result of the above problems, a variety of alternates to a single narrow band arrangement have been developed. For example, a plurality of individual, spaced, bands have been utilized to provide a rather wide elastic area. Also, net arrangements, i.e. cross-connected bands, have been developed. In some instances relatively wide elastic tape arrangements have been proposed. Also, a wide band comprising a plurality of elongate members fused, longitudinally, to one another has also been developed.
While the above-described arrangements have their uses and advantages, none is completely satisfactory. In multiple strand arrangements or net arrangements, attachment to the substrate or garment may pose a problem. A reason for this is that only a relatively narrow point for adhesive attachment is provided, i.e., a point of engagement between a relatively narrow strand member and the wider substrate. A narrow point of adhesion poses a substantial risk of failure, and thus is a problem. Further, multiple strand arrangements can be relatively expensive to construct, as complicated and precise attachment mechanisms and adhesive application arrangements may be required.
Net arrangements may have advantages but can still pose problems, due in part to cost of formation. Also, if thin or narrow strips are used, attachment may still be difficult.
Wide, thick, elastic strips are also not completely satisfactory. In some instances, they may be so thick and strong not to stretch sufficiently for comfort. In other instances, they may be relatively expensive to produce, since a relatively large amount of material may be used in their construction.
A second major method of providing for an elastic strand member on a substrate such as a disposable garment or the like, is through utilization of a strand of heat shrinkable elastic material. Generally, the material is affixed to the substrate in a dimensionally heat unstable state. The substrate and elastic member combination is then exposed to activating heat, to shrink the elastic component and generate gathering or shirring. If properly chosen, the material used for the elastic strand can be provided such that once shrunk it will be appropriately elastic, and thus will stretch around an arm, leg, neck, etc. to provide the desired closing or sealing relationship.
The heat-shrink approach has been utilized in a variety of physical embodiments. For example, multiple strand arrangements may be utilized, as well as net arrangements and the like. In at least one application, multiple strands have been provided within a composite substrate arrangement.
The problems with conventional heat shrinkable elastic strand arrangements have generally been parallel to those described above. If multiple strand arrangements are utilized, they may be relatively complicated to construct or apply. Composite structural relationships may be too expensive for use in many types of disposable items. Problems with placement of adhesive may result, if relatively narrow strands are used. If relatively wide strands are used, there may be problems with insufficient elasticity and/or excessive cost of materials.
It is important to note again that a primary use of elastic strands such as those of concern is to provide for shirring of substrates in disposable garments. It is significant, therefore, to maintain costs at or near a substantial minimum in order to obtain a competitive advantage. Thus, relatively complicated composite arrangements, relatively complicated multi-strand attachment mechanism and relatively difficult to utilize adhesive arrangements are generally to be avoided, if possible. Further, it is preferred to utilize a minimum amount of elastic strand material per substrate or garment, in order to maintain low construction costs. It is important to provide an elastic construction which will be efficient and effective, in order to accommodate the demands of the marketplace and competition.
What has been needed has been an elastic strand construction which is relatively easy to achieve and to mount on or in association with substrates such as disposable garments or the like. Further, what has been needed has been such a strand construction which is efficient and effective in use, to provide for a good, comfortable closing or sealing arrangement when utilized around an arm or leg aperture, or the like. Finally, there has been a need for such an elastic strand which can be manufactured in large quantities relatively quickly, efficiently, and inexpensively.